I have an Ubuntu 12.04.2 server running Xen hypervisor with 2 guests running.

1st guest is a Windows Server 2008 R2 server running DHCP & DNS services.

2nd guest is a Debian squeeze server with just a basic install.

Both are connected to the same bridge on the host which is then connected to eth0 on the host for network access.

The problem I am having is that the Debian guest will not get a DHCP address from the Windows guest running on the same host. I know that the Windows server is giving out DHCP addresses to other devices external to the Ubuntu host, but the Debian guest will not receive an address.

If I manually set an address to the Debian guest I can ping external to the host and also to the Windows server guest so networking seems to be ok. If I run a Windows server VM on a different host (running Virtualbox) then the Debian guest will get an address.

I have also tried with an Ubuntu guest on the same host but this also does not receive an address.

It's quite a strange one, it seems network traffic is passing through ok except for DHCP.